A poultry worker infected with the H7N9 strain of avian influenza died in Shanghai, and three more cases are suspected in the city, China’s official Xinhua News Agency reported today. The virus has infected at least 11 people, killing four of them since China’s health ministry reported the first cases last month, the wire service said.

There’s no evidence of human-to-human transmission of the virus, the agency said. The extent of the outbreak, the source of infection and the mode of transmission are being investigated, and it’s too early to tell whether the cases may signal a pandemic, according to the WHO.

“Until we know what the source of infection is, it’d be premature to say one way or the other,” Gregory Hartl, a WHO spokesman in Geneva, where the organization is based, said by phone yesterday. “We wouldn’t be dealing with a full deck.”

The poultry worker who died was a 48-year-old man who had symptoms including coughing and a fever, Xinhua reported. About eight people had had close contacts with the man, and none have shown unusual symptoms, the news service said.

He is the second person who works with poultry known to have H7N9. China Central Television reported April 2 that a woman who slaughtered birds at a farmers’ market contracted the bird-flu strain.

Pigeon Samples

The H7N9 strain was detected in pigeon samples collected at a marketplace in Shanghai, Xinhua said, citing China’s Ministry of Agriculture. Data from the ministry had shown that a total of 25 H7N9 bird flu strains have been found in wild birds around the world, according to Xinhua.

Concerns that the spread of infections may prompt consumers to eat less poultry led soybeans to decline for a second day. Soybean meal is a primary ingredient in chicken feed. The contract for May delivery lost as much as 0.7 percent to $13.71 a bushel on the Chicago Board of Trade and was at $13.74 by 3:17 p.m. London time. Futures fell 1 percent yesterday.

Drug Demand

The new virus is sensitive to Roche’s Tamiflu and Glaxo’s Relenza treatments, Hartl said.

“There was some initial doubt but those doubts seem to have been put aside after a lot of work done in our collaborating center in Beijing,” he said.

Roche will provide an update on demand for Tamiflu when it reports quarterly sales, Daniel Grotzky, a spokesman for the Basel, Switzerland-based company, said in an e-mail. David Daley, a spokesman for London-based Glaxo, declined to comment on demand for Relenza.

Shanghai issued a level-3 flu alert on April 2, the second- lowest of four levels, following the deaths of the two men, ages 87 and 27, in China’s financial hub last month.

Investigations still haven’t uncovered how the two men contracted the virus, and tests have yet to prove whether it can be transmitted among humans, Wu Fan, head of the city’s disease control center, said at a briefing that day.

Flu Alerts

The discovery of the new virus has prompted other cities in the region to intensify checks. Beijing, the Chinese capital, started monitoring for H7N9 influenza, Xinhua reported, while Taiwan’s Central News Agency said March 31 the island is on the alert for the bug. Officials in Hong Kong activated the alert response level, the lowest of three in the island’s pandemic preparedness plan, and advised people to avoid direct contact with birds.

China’s Center for Disease Control and Prevention advised people against slaughtering poultry for ancestral worship as part of the Tomb-Sweeping holiday that starts today, Xinhua reported yesterday.

The new strain of H7N9 hasn’t previously appeared in humans, the WHO said. The virus’s genetic sequence shows it’s a combination of an H7N9 virus that circulates in birds and an H9N2 pathogen, the European Centre for Disease Prevention and Control said in a report yesterday.

Past Pandemics

The flu pandemics of the past century, including the 1918 Spanish flu that killed as many as 50 million people, have all been triggered by the mixing of human and animal flu viruses to create new pathogens to which people have no pre-existing immunity.

More than 600 people have been infected with the H5N1 bird flu strain since 2003, and almost 60 percent have died, according to the WHO. Most had direct contact with infected poultry, and the virus hasn’t acquired the ability to spread easily between people.

The H1N1 virus responsible for the 2009 swine flu pandemic originated in pigs, then mixed with human and avian viruses, touching off the first global influenza outbreak in more than 40 years and killing about 284,500 people, according to the U.S. Centers for Disease Control and Prevention.